Coating Structure for Obtaining Print Gloss, 1997 Coating Conference Proceedings

This study investigated the influence of the coating structure and the surface properties of ultra-high gloss sheets on offset print gloss. A comparison was made between print gloss for commercial No. 1 grade coated paper, commercial cast coated papers, cast coated test samples, and PET film. Examination of the respective coating structures with mercury porosimetry, oil absorbency and surface analysis by SEM shows that some of these cast coated papers have quite different surface pore structures from the middle to the bottom of the coated layer. The print gloss is affected by the surface coating pore structure rather than the inner pore structure. The lower pore area ratio of the surface prevents rapid absorbency of the ink solvent during the initial period of the ink setting, and causes the high print gloss. Interestingly, PET film, having the highest sheet gloss and almost no surface pores, shows relatively low print gloss. From the SEM observation, it is considered that the splitting pattern of the ink causes the rough surface after printing. These results give us some possibility of obtaining extremely high print gloss paper with acceptable set-off levels, if and when we control the coating structure to be “ small pores on the surface with a large internal pore volume.”